Existing energy storage devices, such as batteries, fuel cells, and electrochemical capacitors, typically have planar architectures with an actual surface area of each component being roughly equivalent to a geometrical area, with a porosity being responsible for any area increase over the geometrical area.
FIG. 1 shows a cross sectional view of an existing energy storage device, a lithium-ion battery 15. The battery 15 includes a cathode current collector 10, on top of which a cathode 11 is assembled. This layer is covered by a separator 12, over which an assembly of an anode current collector 13 and an anode 14 are placed. This stack is then sometimes covered with another separator layer (not shown) above the anode current collector 13, and is then rolled and stuffed into a can to assemble the battery. During a charging process, lithium leaves the cathode 11 and travels through an electrolyte in the separator 12 as a lithium ion into the anode 14. During a discharge process, the lithium leaves the anode 14, travels through the separator 12 and passes through to the cathode 11. The cathode current collector 10 and anode current collector 13 typically can weigh from 5-25% of the battery weight reducing the overall energy density of the battery accordingly.
Three dimensional energy storage devices can produce higher energy storage and retrieval per unit geometrical area than conventional two dimensional (planar) devices. A three-dimensional energy storage device can be one in which any one (or more) of an anode, a cathode, and a separator are non-planar in nature, and an actual surface area for such non-planar component is greater than twice its geometrical surface area. In some instances, a separation between two height planes on a third dimension should be at least greater than a periodicity in an x-y plane divided by a square root of two. For example, for a 1 cm×1 cm sample, a geometrical surface area is 1 cm2. However, if the sample is not flat but has a groove in a depth dimension whose depth is greater than one divided by the square root of two, or 0.707 cm, then its actual surface area would be greater than 2 cm2. Three dimensional energy storage devices also have a decided advantage in providing a higher rate of energy retrieval than planar counterparts for a specific amount of energy stored, such as by minimizing or reducing transport distances for electron and ion transfer between an anode and a cathode. These devices can be more suitable for miniaturization and for applications where a geometrical area available for a device is limited and where energy density requirement is higher than what can be achieved with a planar device.
Three-dimensional energy storage devices, like planar devices, use current collectors to collect the electrical energy generated by the energy storage device and connect it to an outside device so that the outside device can be electrically powered.